Sealing on a fabricated square face
Sealing on a fabricated square face
(OP)
Good Morning,
I have a question regarding sealing on a fabricated square face.
The part is formed / fabricated from sheet metal (2mm). Do you think it is feasible to create the flatness & surface finish on the green face to achieve a seal using a flat face gasket? Can you control the forming process to achieve parallel and flat face on all 4 sides? This isn't machined so will have the standard finish of rolled sheet. The corners are linished / polished to create a flat surface from the weld.
Many Thanks
I have a question regarding sealing on a fabricated square face.
The part is formed / fabricated from sheet metal (2mm). Do you think it is feasible to create the flatness & surface finish on the green face to achieve a seal using a flat face gasket? Can you control the forming process to achieve parallel and flat face on all 4 sides? This isn't machined so will have the standard finish of rolled sheet. The corners are linished / polished to create a flat surface from the weld.
Many Thanks





RE: Sealing on a fabricated square face
RE: Sealing on a fabricated square face
I understand that I will need to use a face gasket. The lid is / will be screwed down. I'm concerned about the manufacturing of the part and the ability to achieve flatness / parallelism & surface finish for a suitable seal.
Thanks again
RE: Sealing on a fabricated square face
RE: Sealing on a fabricated square face
As it stands this is low quantity (prototype), but eventually should be for higher quantity's. So as it stands this is going to have to be 1mm solid gasket i.e. Silicone / EPDM. We have 36 fasteners spaced around and are hoping to achieve 0.3mm compression on the face gasket. This has to create a full seal for all the ingress and egress that you mention. The lid uses M3 screws and is 5mm thick. Currently using C/SINK screws M3 x 12.
What do you mean by 'dead nuts'?
Great response with all the questions I was expecting.
Thanks
RE: Sealing on a fabricated square face
But first.
What fluid is being sealed?
What pressure difference?
What liquid (gas ?) leakage is acceptable and safe? A furnace inlet filter or fan outlet cover has little ( if any) safety impact if a little leaks. Small leaks may have tremendous cost impact if the leaked material has economic costs, or enviro penalties associated with dripped fluids on the ground. Food or medicine requires near-perfect cleanliness at some times, but merely adequate seals in bulk handling material at other times in the process.
Bulk material may not leak at all.
If the opposing surface is flat and strong (like a flanged piece of casting or equipment), the light 2 mm thick piece of sheetmetal - even if machined perfectly somehow at great expense! - will twist and conform to the other surface. So machine the other surface adequately, add a soft gasket material compatible with your product and pressure, and let it bend.
RE: Sealing on a fabricated square face
The pressures are minimal (10 mbar). Temperatures up to 70°C. The 2mm sheet has a 'runner bar' underneath the sealing face allowing for extra thread length.
With regards to what is acceptable or safe leakage. We are trying to achieve the minimum possible leakage, as the liquid we use is a engineered fluid which evaporates very quickly. Hence the bare minimum leakage rate required.
If we have to use a solid rubber EPDM, do you think it is feasible to seal on a sheet metal formed surface? Is it possible with the correct 'jig' to achieve a flat parallel surface on a sheet metal formed part?
Many Thanks
RE: Sealing on a fabricated square face
RE: Sealing on a fabricated square face
Stiff is far more important.
"Bare minimum"is not a quantified engineering requirement.
RE: Sealing on a fabricated square face
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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Sealing on a fabricated square face
Everything leaks - this is true. So with my acceptable leak rate figure I can then conclusively design a part to achieve this? My uncertainty isn't relative to whether the gasket and clamping force could achieve the leak rate, it is whether or not a sheet metal formed surface can be manufactured to create a capable finish for a sealing surface with regard to keeping things flat, parallel etc (lets say for a 1mm solid rubber gasket). Do you think its feasible to manufacture the 4 formed sealing faces flat relative to each other (0.1mm). The ideal scenario is I have fully machined faces to seal on nice thick flanges. However, this currently isn't an option.
Thanks
RE: Sealing on a fabricated square face
RE: Sealing on a fabricated square face
Does not matter how perfectly flat things could be in the as-manufactured free state.
It will not stay flat when you tighten it.
RE: Sealing on a fabricated square face
How much force is needed to achieve the 0.3 mm compression?
For fun I'd be using the free statics FEA program in Solidworks or Creo/Wildfire to see what happens when a 300 lb load is applied to each bolt hole with the gasket replaced by the minimum sealing pressure the gasket maker says they need.
I agree, welded = bent and distorted.
If the cover does not have to be removed very often, formed in place gaskets can be a great solution.
With just about any gasket I'd be contemplating standoffs at each bolt hole to limit the compression.
If the fasteners are 3mm Ø, the width of the gasket inboard of the fastener hole ain't very wide. The gasket width at the two mystery holes near the corners is virtually nil.
RE: Sealing on a fabricated square face
RE: Sealing on a fabricated square face
The M3 screws are tightened using a pozi driver. There are compression limiters in the lid which bottom out at the desired 0.3mm compression. Formed in place gasket would be good, however it means scrapped part once the gasket becomes unusable?
I am guessing the answer is its very hard to achieve flatness and within 0.1mm between 4 faces created in 4 different operations on an cnc air brake.
If I could change to a thicker foam gasket it is what I would do and may have to do. This does have implications though for my design and isn't as straight forward as just replacing from solid to foam.
RE: Sealing on a fabricated square face
Could you elaborate please? The lid needs to be removable.
Many Thanks
RE: Sealing on a fabricated square face
Once per shift, twice a year, every 3 years, every 100,000 miles ?
Formed in place gaskets don't destroy the parts. Some formulations can be tough to remove from the components.
Most Any gasket needs some width to perform ( seal) .. The attached image shows regions of the flange on your rendered image that look mighty narrow to me.
Here is a link to a paper gasket that seals quite reliably. The components are machined castings, but the area is generous.
https://www.nwmaicocz.com/maico-parts/pc/catalog/b...
There is such a thing as too much area, when the clamping contact pressure ( psi) is too low.
Makers of gasket materials have some pretty detailed info about such matters, to ensure the gasket is clamped everywhere
I expect There needs to be a compression limiter surrounding each fastener. A limiter midway between fasteners, or every now and then can make distortion matters worse.
"Great response with all the questions I was expecting."
If you were expecting some of these questions it would have been more efficient to provide answers in the OP.
It is not too late to pre-emptively answer all the questions you are still expecting.
RE: Sealing on a fabricated square face
Sealant, not adhesive. Removal of your cover will not be a problem.
Wet sealant also means you don't have to tool and produce a custom gasket.
RE: Sealing on a fabricated square face
gasket maker
Silicone RTV
form a gasket
Permatex
ect.
https://www.mcmaster.com/#silicone-gasket-sealants...
There are even conductive ones if you need a EMC seal.
Here is a design guide.
https://www.permatex.com/heres-how/product-guide/
RE: Sealing on a fabricated square face
From what I was told the curing process uses hydrogen mainly out of the air.
To speed up the curing you can mist it with water. H2O
To slow the process spray it with mineral sprits.
If you apply the silicone and mist it you can create a "Skin" before you assemble the parts.
You can also apply something like wax as a bond breaker on the mating part.
If time allows, let the silicone set up for awhile after assembling before final tightening of the bolts.
It's something you'll need to experiment with.
RE: Sealing on a fabricated square face
I wonder what he has been trying.
RE: Sealing on a fabricated square face
I was reminded of the old Chevy valve covers that long ago had bolts on the perimeter which most of us ended up putting shaped "Washers" under to help seal the cover.
Now they only have two bolts on the center line of the cover and a torque specification for the two bolts.
Neither one of my 350's has a leak from the valve covers even with more than 200,000+ miles on them.
RE: Sealing on a fabricated square face